1. Field of the Invention
This invention relates to polyurethane resins and is more particularly concerned with blends of polyurethane resins containing a minor amount of a second polymer which is incompatible therewith.
2. Description of the Prior Art
Clear polyurethane resins, produced by reaction of an organic polyisocyanate and a low molecular weight active hydrogen containing compound such as an aliphatic glycol, have been known in the art for a considerable time; see, for example, O. Bayer, Angewandte Chemie, 59, No. 9 at pp 255-288, September 1947. These materials are rigid and relatively brittle, i.e. they demonstrate a low order of impact resistance when tested in accordance with standard tests such as the Notched Izod impact test (ASTM D256-56). Accordingly, they have found relatively little application in the fabrication of structural components such as automobile body parts, equipment housings, mechanical goods and the like.
Various methods for modifying the properties of such resins have been suggested. Illustratively, U.S. Pat. No. 4,076,660 describes the production of rapid-setting rigid polyurethanes by reacting an organic polyisocyanate, an aliphatic monomeric triol and a low molecular weight propylene glycol derivative in the presence of a modifier which is a liquid carboxylic acid ester. The resulting products are said to be moldable by casting to form machine parts and the like. U.S. Pat. No. 4,076,679 shows making similar compositions but using, as the modifier which is incorporated into the polyurethane-forming reaction mixture, a polymer derived from one or more ethylenically unsaturated monomers which polymer is in the form of a liquid or a grease meeting certain specifications.
U.S. Pat. No. 4,342,847 describes a process for the preparation of thermoplastic materials by introducing a thermoplastic polymer into an extruder at a first inlet at a temperature such that the polymer melts and then adding polyurethane forming reactants through a second inlet. The blend of the thermoplastic polymer and the polyurethane is discharged from the extruder in finished form. The resulting polymer blend is said to possess high impact resistance. Examples 1(a), (b) and (c) and 2(b) of the reference show the use of an ABS polymer as the thermoplastic polymer and butanediol and various diisocyanates (but no polyol) as the polyurethane forming reactants. The minimum amount of ABS polymer used in these various Examples is 39.3 percent by weight based on total weight of the ABS polymer and the polyurethane. Example 2(d) serves to demonstrate that the high impact proporties are not achieved if the polyurethane is formed first and the thermoplastic polymer is added later.
It has now been found that polymers having properties comparable to those of engineering plastics such as nylon and the recently reported polyurethanes of U.S. Pat. No. 4,376,834, can be obtained by blending a clear polyurethane plastic with a minor amount of certain impact modifiers which are incompatible with the polyurethane.